This invention relates to a method of forming a contact bump.
In order to provide a good, electrically-conductive connection between, for example, a contact pad of a circuit board and a contact pad of a hybrid circuit, it is conventional to form a bump on one of the contact pads. The effect of the bump is to increase the contact pressure for a given contact force and thereby reduce the contact resistance between the pad of the hybrid circuit and the pad of the circuit board.
It is conventional to form a bump on a pad of a circuit board by plating metal onto the contact pad. Generally, gold is selected as the metal for the bump because it does not corrode and therefore its contact resistance does not change with time. However, a relatively large volume of gold is required in order to provide a given contact area, and therefore use of plated-up gold contact bumps is expensive. Moreover, it is very difficult to control the plating process in order to obtain bumps of a desired, e.g. part-spherical, shape.